Evaluate the efficacy of a number of retinoids of differing chemical structures to prevent the development of bladder cancer during its preneoplastic period using the FANFT model for bladder cancer induction. Determine effects of retinoids on the bladder and on tumor development by using the following parameters: bladder weight; number of tumors per bladder detected grossly; percent of bladder having hyperplasia, papilloma, and carcinomas (staging of urinary bladder pathology will be based on the World Health Organization); and recording of other pathological lesions, including other tumors. Monitor FANFT in the feed or ANFT in the urine by quantitation of Salmonella typhimurium revertants produced by urine of experimental animals. Monitor blood and tissue levels of retinoids in experimental animals.